The present invention relates to optical waveguides, and more particularly to a method capable of forming a plurality of optical waveguides in a single, monolithic structure.
It has long been known that elongate optical waveguides may be formed by heating a cylindrical blank of transparent dielectric material, such as glass, and drawing the end of the blank into a thin, elongate structure.
According to one currently accepted practice a drawing blank is formed by coating a rotating, cylindrical starting member with a sinterable glass soot. The soot is built up, layer by layer, by traversing the length of the rotating starting member with a hyrolyzing flame. The soot coating is laid down along a spiral locus, the various layers merging together to form a continuum. One such process is described in U.S. Pat. No. 2,272,342 -Hyde and U.S. Pat. No. 2,326,059-Nordberg. In order to provide a cladding exhibiting a different index of refraction than the center portion (core) of the member, a second composition is applied by the hydrolysis technique to complete the process. The second composition, when fused, exhibits a lower index of refraction than the core or first composition, the interface between the compositions serving to define the boundaries of a waveguide within which optical signals may propagate.
It has been recognized that it would be advantageous to provide a number of discrete waveguide cores in a single, monolithic structure, wherein the cores share a common cladding matrix. It has been proposed that discrete core and cladding strands be formed, and the cladding strands placed about the core strand and extruded or otherwise operated upon to form a single monolithic structure. Such an approach is disclosed in U.S. Pat. No. 3,930,714-Dyott. Preforming a plurality of cores having cladding thereon and then drawing the preformed cores together to cause the claddings to fuse is disclosed in the prior art, as for instance in U.S. Pat. No. 2,992,516 - Norton. The formation of a multi-core waveguide from a monolithic drawing blank has not, however, been successfully accomplished by workers in the field.
A further problem which has occurred in the prior art methods of building up successive, spirally-oriented layers of glass soot upon a starting member is the helical pattern which sometimes develops upon the surface of the starting member. Accordingly, it will be appreciated that it would be highly desirable to provide a method for eliminating an uneven buildup of material upon the outer surface of the starting member during a soot deposition process, and to provide a method whereby a plurality of waveguide cores could be formed in a single, monolithic drawing blank.
It is therefore an object of the present invention to provide a method for forming a starting blank embodying a plurality of waveguide core elements.
It is another object of the present invention to provide a method for forming an elongate waveguide structure embodying a plurality of core members.
Yet another object is to provide a method of forming one or more helically-oriented waveguides within a common cladding member.
Another object of the invention is to provide a method of depositing sinterable material upon a starting member in a uniform manner to obtain a substantially ripple-free surface.
Still another object is to provide a waveguide system including one or more helically-disposed core elements enveloped by a common cladding.